Vehicles having a hybrid drive in which various drives are used for the drive function are increasingly being developed. In this connection, the individual motors are able to cooperate in different ways in the hybrid drive.
They function either simultaneously or only one drive unit acts on the vehicle to be moved.
Frequently, the hybrid drive in a motor vehicle is made up of an internal combustion engine and an electric motor. In this case, the rotor temperature of the electric motor must be constantly monitored to ensure that this component is protected.
In motor vehicle technology, it is unsuitable to measure the rotor temperature of the electric motor using a temperature sensor due to insufficient space for a temperature sensor or excessively high costs. For that reason, the rotor temperature is calculated using a temperature model, the rotor temperature being a function of the magnetic flux linkage. As the magnets of the electric motor are demagnetized in an excessively heated motor and accordingly the magnetic flux is changed, this results in an incorrect calculation of the rotor temperature.
German Patent No. DE 102 54 295 describes calculating the rotor temperature in permanently excited polyphase machines based on an instantaneous no-load voltage and a reference no-load voltage.
An object of the present invention is therefore to provide a method and a system for determining the rotor temperature of an electric motor of a hybrid vehicle in which reliable determination of the rotor temperature is possible using simple means.